The configuration of human teeth requires that the ideal bristle contour for toothbrushes for brushing the buccal or outside surfaces of teeth be concave and that the ideal bristle contour for brushing the lingual or inside surfaces of teeth be convex. Most brushes have a single piece head which is of comparable thickness to the handle and which, consequently, is relatively rigid and of a fixed curvature or configuration. Some brushes may, however, incorporate a means for allowing the head to flex relative to the handle, as described for example in EP-A-371,293. Even so, such brushes have limited effectiveness. Other brushes are known which are adjustable into several different but fixed configurations. Adjustable toothbrushes are often difficult to manipulate and may be unreliable.
A further drawback of conventional brushes is that pressing the brush sufficiently hard against the teeth to get good cleaning risks damaging or discomforting the softer, adjacent gums. To a certain extent this can be solved by modifying the configuration of the brush, or by varying bristle hardness or length, though again, a single configuration cannot be optimum for all circumstances.
U.S. Pat. No. 4,712,267, issued to Cheng, discloses a convertible toothbrush comprising an S-shaped elongated handle of shape-retaining material having curved end regions of opposite curvature, a flexible brush block containing bristles, and a means for mounting the flexible brush block on the handle for longitudinal movement along the length of the handle. The curved portions of the handle bend the flexible block and bristles into a concave or convex configuration which corresponds to the curved configuration of the handle.
EP-A-454,625, assigned to Warner-Lambert Company, describes an adjustable curvature toothbrush whose head is in the form of a loop. A cam or slide mechanism changes the curvature of the head between concave and convex configurations. In an alternative embodiment, the head is an integral part of the handle which is in the form of a compressible closed loop, the bristle surface being in a concave configuration when the handle is in its uncompressed state, becoming convex when the handle is compressed.
EP-A-577,656, to Linsner & Fischer GmbH, discloses a toothbrush having a handle and at one end thereof a bristle-bearing head, wherein the head is in the form of two or more segments flexibly and resiliently linked to each other and/or to the handle, one or more of the segments being bristle bearing. In one embodiment this is achieved by the use of transverse, and optionally longitudinal, grooves on the opposite face of the head to the bristles. Under application of pressure in use the brush head may adopt a convex configuration. In another embodiment the handle extends into a frame into whose interior the head is resiliently linked. When pressure is applied to the centre of the brush head it adopts a concave configuration.
While the above toothbrushes provide brush heads with some degree of flexibility, none of them is entirely satisfactory, in particular, they either fail to provide both convex and concave configurations within the one embodiment or they require undue manipulation or skill on behalf of the user.
It is accordingly an object of this invention to provide a toothbrush with a head which can flexibly conform to either the convex or concave surfaces of the teeth and which provides good cleaning and is easy to manufacture and use.
It is a further object of the invention to provide a toothbrush which can clean the teeth efficiently with minimal damage to adjacent gum tissue.